All questions of Computer Networks for Computer Science Engineering (CSE) Exam

Routing information protocol

Interactive games
Interactive games stand out as the odd one out among the given options.

File transfer
File transfer refers to the process of moving data from one device to another, either locally or over a network. It is a common task in computing.

File download
File download is the action of retrieving data from a remote system or the internet and saving it to a local device for later use. It is a common feature in web browsers and other applications.

E-mail
E-mail, short for electronic mail, is a method of exchanging digital messages over the internet. It is widely used for communication purposes.

Interactive games
Interactive games involve user engagement and participation in a virtual environment, typically for entertainment or educational purposes. Unlike the other options, interactive games are focused on providing a fun and immersive experience rather than data transfer or communication.

Answer:


When it comes to delivering and storing mail on a receiver server, the protocol that is commonly used is the Simple Mail Transfer Protocol (SMTP). SMTP is responsible for sending outgoing mail from the sender's server to the recipient's server. It is a standard protocol used for email transmission over the internet.


SMTP is designed to handle the delivery of email messages. It operates on the application layer of the TCP/IP protocol suite and uses a client-server model. Here's how SMTP works:

1. Connection Establishment: The email client (sender) establishes a connection with the email server (SMTP server) on port 25.

2. Handshaking: The client and server exchange a series of commands and responses to establish a connection. This includes the identification of the client and server, as well as the negotiation of supported features and security options.

3. Email Transfer: Once the connection is established, the client sends the email message to the server using SMTP commands. This includes the sender's email address, recipient's email address, subject, and the contents of the email.

4. Mail Delivery: The server verifies the email addresses, checks for spam or security issues, and then attempts to deliver the email to the recipient's server.

5. Error Handling: If there are any errors or issues during the email transfer process, SMTP provides error codes and messages to help diagnose and resolve the problem.

6. Store and Forward: SMTP supports the concept of "store and forward," meaning that if the recipient's server is unavailable or offline, the email can be stored on the sender's server until the recipient's server becomes accessible. Once the recipient's server is available, the email will be delivered.


In summary, SMTP is the protocol responsible for delivering and storing mail on a receiver server. It provides a reliable and standardized method for sending email messages over the internet. By following the SMTP protocol, email clients and servers can communicate and ensure that email messages are successfully delivered to the intended recipients.

Domain Name System (DNS)
The Domain Name System (DNS) is a decentralized naming system for computers, services, or any resource connected to the Internet. It translates easily memorizable domain names to the numerical IP addresses needed for locating and identifying computer services and devices with the underlying network protocols.

Function of DNS
- Translate Domain Names: DNS translates human-friendly domain names (like www.example.com) into IP addresses that computers can understand.
- Mapping IP Addresses: It maps domain names to IP addresses and vice versa, enabling users to access websites and other online resources by typing in a domain name.
- Load Balancing: DNS can distribute incoming network traffic across a group of servers, helping to balance the load and ensure optimal performance.
- Redundancy and Fault Tolerance: DNS can provide redundancy by having multiple servers handling DNS requests, ensuring that if one server fails, others can step in to resolve domain names.

Importance of DNS
DNS is a critical component of the Internet infrastructure as it simplifies the process of accessing websites and services by allowing users to use domain names instead of remembering complex IP addresses. It plays a crucial role in ensuring the smooth operation of the Internet and is indispensable for modern communication and online activities.
In conclusion, the Domain Name System (DNS) is responsible for translating domain names to IP addresses, making it possible for users to access websites and services on the Internet. It is a fundamental technology that underpins the functionality and usability of the Internet as we know it today.

Baud is a term used in digital communication to refer to the rate at which the signal changes. It is not directly related to the number of bits or bytes transmitted per unit time. Baud is a measure of the signaling rate or the number of signal events per second. Let's understand this concept in detail.

Understanding Baud

The term "baud" was originally used to indicate the number of signaling events per second in analog communication systems. In digital communication, baud refers to the number of signal events per second as well. However, in digital communication, each signal event can represent multiple bits.

Bits and Baud

In digital communication, the number of bits transmitted per unit time depends on the modulation scheme used. Modulation is the process of encoding information into a carrier signal. Different modulation schemes allow multiple bits to be represented by a single signal event.

For example, in a binary modulation scheme like binary phase-shift keying (BPSK), each signal event represents one bit. So, in this case, the number of bits transmitted per unit time is equal to the baud rate.

However, in more complex modulation schemes like quadrature amplitude modulation (QAM), each signal event can represent multiple bits. For instance, in 16-QAM, each signal event represents 4 bits. In this case, the number of bits transmitted per unit time is higher than the baud rate.

Conclusion

To summarize, baud refers to the rate at which the signal changes in digital communication. It is not directly related to the number of bits or bytes transmitted per unit time. The number of bits transmitted per unit time depends on the modulation scheme used. Baud is still important in digital communication as it indicates the rate at which the signal events occur, which has implications for the bandwidth and data rate of a communication system.

A packet-switching network:

Packet-switching is a method of transmitting data over a network in which messages are divided into small packets. These packets are then individually sent across the network and reassembled at the destination. This approach is different from circuit-switching, where a dedicated communication path is established for the entire duration of the transmission.

Advantages of a packet-switching network:

A packet-switching network offers several advantages over other networking approaches, such as:

1. Reduced cost: Packet-switching networks can significantly reduce the cost of using an information utility. This is because they allow multiple users to share the same communication channels, resulting in more efficient use of network resources.

2. Shared channels: In a packet-switching network, communications channels can be shared among more than one user. This means that multiple users can send packets simultaneously over the same channel, increasing the overall network capacity and improving efficiency.

3. Flexibility: Packet-switching networks are highly flexible and can handle various types of data, including voice, video, and text. This versatility makes them suitable for a wide range of applications and allows for efficient transmission of different types of information.

4. Error detection and correction: Packet-switching networks often incorporate error detection and correction mechanisms. Each packet is typically accompanied by checksums or other error detection codes, which allow the receiver to verify the integrity of the data. If errors are detected, the receiver can request retransmission of the affected packets, ensuring reliable data transmission.

5. Scalability: Packet-switching networks can easily accommodate a growing number of users and increasing data traffic. As more users join the network, additional packets can be transmitted simultaneously, providing scalability and adaptability to changing network demands.

6. Efficient use of network resources: Packet-switching networks make efficient use of network resources by dynamically allocating bandwidth to users as needed. This allows for optimal utilization of available resources and prevents underutilization or congestion.

In conclusion, a packet-switching network offers numerous benefits, including reduced cost, shared channels, flexibility, error detection and correction, scalability, and efficient use of network resources. These advantages make packet-switching networks a preferred choice for modern communication systems.

The TCP/IP model and the OSI model are two different conceptual models used to understand and describe how network protocols work. The TCP/IP model is a simpler and more practical model that is widely used in real-world networking, while the OSI model is a more theoretical and detailed model.

The TCP/IP model consists of four layers:

1. Network Interface Layer: This layer deals with the physical connection between the network device and the network medium. It defines how data is transmitted over the physical network, including the protocols used for addressing and error detection.

2. Internet Layer: This layer is responsible for routing packets across different networks. It uses IP (Internet Protocol) to address and route packets between different hosts on the internet.

3. Transport Layer: This layer is responsible for the reliable delivery of data between hosts. It provides mechanisms for establishing connections, breaking data into smaller packets, reassembling packets at the receiving end, and ensuring that data is delivered without errors or loss.

4. Application Layer: This layer is responsible for supporting specific network applications and protocols. It includes protocols such as HTTP (Hypertext Transfer Protocol), FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), and DNS (Domain Name System).

On the other hand, the OSI model consists of seven layers:

1. Physical Layer: This layer deals with the physical transmission of data over the network medium, including electrical and mechanical specifications.

2. Data Link Layer: This layer provides error-free transmission of data frames between two adjacent nodes over a physical network. It includes protocols such as Ethernet and Wi-Fi.

3. Network Layer: This layer is responsible for routing packets across multiple networks. It includes protocols such as IP (Internet Protocol) and ICMP (Internet Control Message Protocol).

4. Transport Layer: This layer provides reliable end-to-end delivery of data between hosts. It includes protocols such as TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

5. Session Layer: This layer establishes, manages, and terminates communication sessions between applications. It includes protocols such as NetBIOS (Network Basic Input/Output System).

6. Presentation Layer: This layer is responsible for the formatting and presentation of data to the application layer. It includes protocols such as SSL (Secure Sockets Layer) and MIME (Multipurpose Internet Mail Extensions).

7. Application Layer: This layer supports specific network applications and protocols. It includes protocols such as HTTP, FTP, SMTP, and DNS.

According to the question, the TCP/IP model does not have a session layer, while the OSI model does have a session layer. The session layer in the OSI model is responsible for managing communication sessions between applications, while the TCP/IP model combines this functionality into the application layer.

Routing protocols can be divided into 2 categories:

1. Interior Gateway Protocols (IGPs):
- IGPs are used within an autonomous system (AS), which is a network under a single administrative domain.
- These protocols are responsible for exchanging routing information between routers within the same AS.
- Examples of IGPs include Routing Information Protocol (RIP), Open Shortest Path First (OSPF), and Intermediate System to Intermediate System (IS-IS).

2. Exterior Gateway Protocols (EGPs):
- EGPs are used to exchange routing information between different autonomous systems.
- These protocols enable routers in different ASes to communicate and determine the best path for forwarding traffic between them.
- The most commonly used EGP is the Border Gateway Protocol (BGP), which is used in the global Internet.

Explanation:
Routing protocols are used by routers to exchange routing information and determine the best path for forwarding packets. They play a crucial role in ensuring efficient and reliable packet delivery in a network. These protocols can be categorized based on the scope of their operation.

Interior Gateway Protocols (IGPs) are used within a single autonomous system (AS). An AS is a network under a single administrative domain. IGPs are responsible for exchanging routing information between routers within the same AS. This allows routers to build and maintain a routing table that contains information about the network topology and the best path to reach different destinations within the AS. Examples of IGPs include RIP, OSPF, and IS-IS.

Exterior Gateway Protocols (EGPs), on the other hand, are used to exchange routing information between different autonomous systems. EGPs enable routers in different ASes to communicate and determine the best path for forwarding traffic between them. This is particularly important for interconnecting multiple ASes, such as in the case of the global Internet. The most commonly used EGP is BGP, which is responsible for exchanging routing information between ASes and determining the best path for traffic to traverse between them.

In summary, routing protocols can be divided into 2 categories: IGPs, which are used within a single AS, and EGPs, which are used to exchange routing information between different ASes.

Propagation Time:
Propagation time can be calculated using the formula:
Propagation time = Distance / Propagation Speed
Given that the distance is 3000 km and the propagation speed is 6 jasec/km, we can calculate the propagation time as follows:
Propagation time = 3000 km / (6 jasec/km) = 500 jasec

Transmission Time:
Transmission time can be calculated using the formula:
Transmission time = Frame size / Trunk data rate
Given that the frame size is 64 Bytes and the trunk data rate is 1.544 Mbps, we need to convert the frame size to bits and the data rate to bps:
Frame size = 64 Bytes * 8 bits/Byte = 512 bits
Trunk data rate = 1.544 Mbps * 10^6 bps/Mbps = 1.544 * 10^6 bps
Now we can calculate the transmission time:
Transmission time = 512 bits / (1.544 * 10^6 bps) = 0.000331 s

Efficiency:
Efficiency can be calculated using the formula:
Efficiency = (Window Size * Frame Size) / (Propagation Time + Transmission Time)
We need to find the maximum window size that achieves an efficiency of 100%, so we can set the efficiency to 1:
1 = (Window Size * 512 bits) / (500 jasec + 0.000331 s)
Rearranging the equation:
Window Size = (500 jasec + 0.000331 s) / 512 bits

Calculating Window Size:
Substituting the values:
Window Size = (500 jasec + 0.000331 s) / 512 bits
We need to convert the propagation time to seconds:
Propagation Time = 500 jasec * (1 sec / 10^12 jasec)
Window Size = (500 * 10^12 sec + 0.000331 s) / 512 bits

Simplifying the equation:
Window Size = (500 * 10^12 sec + 0.000331 s) / 512 bits
Window Size = (5 * 10^14 + 0.000331 * 10^12) / 512 bits
Window Size = (5 * 10^14 + 331 * 10^6) / 512 bits
Window Size = (5 * 10^14 + 331 * 10^6) / 512 bits
Window Size ≈ 9.765 * 10^11 bits / 512 bits
Window Size ≈ 1.909 * 10^9

Rounding the Window Size:
Since the window size cannot be a fraction, we round down the window size to the nearest whole number:
Window Size ≈ 1,909,000,000
The maximum window size at the sender's side is approximately 1,909,000,000 bits.

Answer:
The protocol used to convert IP addresses to MAC addresses is ARP (Address Resolution Protocol). ARP is a communication protocol that is used to map an IP address to a physical (MAC) address on a local network.

Explanation:
When a device wants to communicate with another device on the same local network, it needs to know the MAC address of the destination device. However, devices use IP addresses to communicate with each other at the network layer.

Here is how ARP works to convert IP addresses to MAC addresses:

1. ARP Request:
When a device wants to know the MAC address corresponding to a specific IP address, it first sends an ARP request to the local network. The ARP request has the IP address of the desired device and the MAC address of the sending device.

2. Broadcast:
The ARP request is broadcasted to all devices on the local network. This is because the sending device does not know the MAC address of the desired device, so it sends the request to all devices.

3. ARP Reply:
The device with the IP address mentioned in the ARP request responds with an ARP reply. The ARP reply contains the MAC address of the responding device.

4. MAC Address Mapping:
Upon receiving the ARP reply, the sending device updates its ARP cache with the IP-to-MAC address mapping. The ARP cache is a table that keeps track of the IP-to-MAC address mappings for faster future communication.

Benefits of ARP:
- ARP allows devices to dynamically discover the MAC addresses of other devices on the local network, eliminating the need for manual configuration.
- It enables devices to communicate with each other using IP addresses while relying on MAC addresses for actual data transmission.
- ARP helps in optimizing network performance by reducing the time required to resolve IP-to-MAC address mappings.

Conclusion:
ARP is the protocol used to convert IP addresses to MAC addresses. It allows devices on a local network to dynamically discover and map IP addresses to MAC addresses for efficient communication. By using ARP, devices can communicate with each other using IP addresses while relying on MAC addresses for actual data transmission.

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Explanation:

Client as the Source Host:
- When the source host is a client, the port number used is known as an "ephemeral port number."
- Ephemeral port numbers are randomly assigned by the client's operating system from a specific range of port numbers (49152 to 65535).
- These ports are used for outgoing connections to servers on the internet.

Role of Ephemeral Port Number:
- Ephemeral port numbers are temporary and dynamically allocated for the duration of a specific network connection.
- They help in uniquely identifying each connection that a client makes to a server.
- Once the connection is terminated, the ephemeral port number is released back to the pool for reuse.

Client-Server Communication:
- In a client-server communication model, the client initiates a connection to the server using an ephemeral port number.
- The server, on the other hand, uses a well-known port number (e.g., port 80 for HTTP) to listen for incoming connections.

Conclusion:
- In the context of port numbers, when the source host is a client, the port number used is an ephemeral port number.
- This allows for the establishment of unique connections between clients and servers on the internet.

Explanation:

UDP Datagram Length Calculation:
- The correct expression for the length of a UDP datagram is UDP length = IP length – IP header’s length.
- This calculation is based on the structure of the IP and UDP headers in a network packet.

IP Header:
- The IP header contains information about the source and destination IP addresses, protocol being used (UDP in this case), and the total length of the IP packet.

UDP Header:
- The UDP header contains information about the source and destination ports, length of the UDP datagram, and a checksum for error detection.

Explanation of the Calculation:
- When calculating the length of the UDP datagram, we subtract the length of the IP header from the total length of the IP packet.
- This is because the IP length includes both the IP header and the UDP datagram, so subtracting the IP header’s length gives us the length of the UDP datagram.

Example:
- If the total length of the IP packet is 100 bytes and the IP header length is 20 bytes, then the length of the UDP datagram would be 100 - 20 = 80 bytes.

Conclusion:
- Understanding how to calculate the length of a UDP datagram is important for network engineers and developers working with UDP-based applications. By following the correct expression UDP length = IP length – IP header’s length, they can accurately determine the size of the UDP data being transmitted over the network.

Introduction:
The option 'c) Telnet' allows a user at one site to establish a connection to another site and then pass keystrokes from the local host to the remote host. Telnet is a protocol that enables remote access to computers over a network. It provides a virtual terminal connection, allowing users to interact with remote systems as if they were directly connected.

Explanation:
Telnet is a client-server protocol that allows a user to establish a connection with a remote host and communicate with it using a terminal emulation application. Here's how it works:

1. Establishing a connection:
- The user initiates a Telnet session by running a Telnet client application on their local host.
- The user specifies the IP address or domain name of the remote host they want to connect to.
- The Telnet client establishes a connection to the Telnet server running on the remote host.

2. Passing keystrokes:
- Once the connection is established, the user can start passing keystrokes from their local host to the remote host.
- Any keystrokes entered by the user on their local host are sent over the network to the remote host.
- The remote host receives the keystrokes and processes them as if they were entered directly on the remote system.

3. Terminal emulation:
- Telnet provides terminal emulation, which means that the user's local terminal (or terminal emulator) behaves like the terminal on the remote host.
- The remote host sends output back to the user's local host, and it is displayed on the local terminal.
- This allows the user to interact with the remote system in a seamless manner, as if they were physically present at the remote location.

4. Usage:
- Telnet is often used for tasks such as remote administration, troubleshooting, and accessing resources on remote systems.
- It is commonly used for managing network devices, such as routers and switches, as well as accessing remote servers and mainframes.
- Telnet is a simple and widely supported protocol, but it lacks encryption and is considered insecure for transmitting sensitive information.

Cyclic Redundancy Check (CRC) is used for error detection at the data link layer of the OSI model. It is a widely used error detection technique that can detect a variety of errors, including single-bit errors, burst errors, and most other types of common errors.

CRC works by adding redundant bits to the data being transmitted. These redundant bits are generated by performing mathematical calculations on the original data using a predefined polynomial. The sender and receiver both use the same polynomial to perform these calculations.

The steps involved in CRC error detection are as follows:

1. Sender's Perspective:
- The sender treats the data to be transmitted as a binary polynomial.
- The sender appends a predefined number of zeros (equal to the degree of the polynomial) to the end of the data.
- The sender performs a division operation on the polynomial, using the predefined polynomial as the divisor.
- The remainder obtained from the division operation is appended to the original data.
- The sender transmits the original data along with the appended remainder.

2. Receiver's Perspective:
- The receiver receives the transmitted data.
- The receiver performs the same division operation on the received data, using the same predefined polynomial as the divisor.
- If the remainder obtained is zero, it means no errors were detected during transmission.
- If the remainder obtained is non-zero, it indicates that errors were detected during transmission.

CRC is effective in detecting errors because any change in the data during transmission is highly likely to result in a non-zero remainder. The predefined polynomial used in CRC is carefully chosen to maximize the error detection capabilities.

Advantages of CRC for error detection:
- It is simple and efficient to implement.
- It can detect a wide range of errors, including burst errors.
- It has a high probability of detecting errors.

In conclusion, CRC is a widely used error detection technique at the data link layer. It involves adding redundant bits to the data being transmitted and performing mathematical calculations to detect errors. CRC is efficient and effective in detecting a variety of errors, making it a popular choice for error detection in data communication systems.

Simple Network Management Protocol (SNMP)
SNMP is an internet standard protocol used for managing devices on IP networks. Here is a detailed explanation of SNMP:

Overview
- SNMP is commonly used in network management systems to monitor network-attached devices for conditions that warrant administrative attention.
- It allows network administrators to manage network performance, find and solve network problems, and plan for network growth.

Operation
- SNMP works by sending messages, called protocol data units (PDUs), to different parts of a network.
- These messages allow network administrators to manage network performance, find and solve network problems, and plan for network growth.

Components
- SNMP consists of three key components: managed devices, agents, and network management systems (NMS).
- Managed devices, such as routers, switches, servers, and printers, contain SNMP agents.
- Agents collect and store management information and make it available to the NMS.

Features
- Some key features of SNMP include device discovery, monitoring, alerting, and performance analysis.
- It provides a standardized framework for managing any device on the network.
In conclusion, SNMP is a crucial protocol for managing devices on IP networks. It plays a vital role in network management, allowing administrators to monitor and control network devices efficiently.

Understanding Application Layer Protocols
Application layer protocols are vital in the realm of computer networking as they define the rules and conventions for communication between applications. The correct option is 'D'—all of the mentioned components are essential to the functionality of these protocols.
Types of Messages Exchanged
- Application layer protocols specify different types of messages that can be exchanged between communicating entities.
- These messages can include requests, responses, notifications, and error messages, each serving a specific purpose in the communication process.
Message Format, Syntax, and Semantics
- Each message must adhere to a defined format and syntax. This is crucial for ensuring that both the sender and receiver understand the content.
- Semantics refers to the meaning of the messages and the actions that should be taken upon receipt, ensuring that the intended operation is clear.
Rules for Sending and Responding to Messages
- Application layer protocols dictate when and how processes send messages and how they should respond to incoming messages.
- This includes timing, sequence, and conditions under which messages should be sent, which is essential for maintaining the integrity and efficiency of communication.
Conclusion
In summary, application layer protocols encompass a comprehensive set of guidelines that include the types of messages exchanged, their format, syntax, semantics, and the rules governing the communication process. This holistic approach is why the correct answer is 'D'—all of the mentioned components are integral to the functionality of application layer protocols.